1. Field of the Invention
The present invention generally relates to compositions useful for forming articles by means such as thermoplastic processing (e.g., molding, extrusion and casting), and more particularly relates to certain synthetic hydroxy-functional polyester containing compositions hereinafter sometimes referred to as "hydroxy-functional polyester compositions." Articles with good mechanical properties, such as tensile strength and/or tensile elongation, can be made with these synthetic hydroxy-functional polymers in combination with natural polymers. Such articles are biodegradable and have a reduced cost of manufacture due to the inclusion of a low cost natural polymer, such as protein.
More specifically, this invention relates to novel compositions comprising blends of poly(hydroxy ester ether) with various renewable proteins.
2. Background of the Invention
Natural polymers have been the focus of considerable research interest in attempts to use these as fillers in order to decrease polymer costs and to use polymers that are biodegradable. Several recent examples including Uemura et al. (U.S. Pat. No. 5,384,187), Wnuk et al. (U.S. Pat. No. 5,391,423), and Bastioli et al. (U.S. Pat. No. 5,412,005) all represent attempts to achieve biodegradable polymer compositions in which natural polymers such as starches have been added to synthetic polymers. Unfortunately, while the inclusion of natural polymers can reduce costs, the mechanical properties of the synthetic polymer can be so adversely affected by inclusion of the natural polymer as to vitiate the cost advantages.
One successful system for blending thermoplastic polymers with natural polymers relies upon the use of certain hydroxy functional polyethers, also called "polyhydroxy ester ethers" or "PHEE". In WO 97/23564, Mang et al. discloses blending PHEEs with polysaccharides, particularly granular starches. The resulting compositions are disclosed as being useful for making granules that could subsequently be processed into useful articles by injection molding, foaming, film formation and the like.
Xu et al. (U.S. Pat. No. 5,665,786) discloses using the same PHEEs as taught by Mang et al., supra, and starch in the making of thermoformed articles having exterior surfaces that are substantially resistant to moisture. In U.S. Pat. No. 5,821,286, Xu also discloses the use of PHEEs and gelatinized starch in the making of biodegradable films.
Willet et al. (U.S. Pat. No. 5,852,078) produces a composition useful for formed articles from PHEE and granules of starch, a modified starch, or guar gum.
The search continues for alternatives to the aforementioned systems for producing synthetic polymer-based compositions that can be formed into useful articles. Such articles include, for example, disposable plastic utensils or stretchable thin films for food packaging purposes, that are reasonably competitive in price with commodity plastics such as polyethylene or polystyrene, but which are more environmentally friendly and reduce the dependence on petroleum products.